1. Field of the Invention
The present invention generally relates to an optoelectronic sensor device for detecting the degree of precipitation wetting of a transparent pane in which the optoelectronic sensor device has a beam guide body associated with beam transmitters and receivers arranged on a main board and a heating device located in an area lying outside of the beam paths of the beam transmitters and receivers.
2. Background Art
Optoelectronic sensor devices are typically employed to influence a windshield washer system as a function of the amount of precipitation located on the windshield of a motor vehicle. Such devices generally employ a beam transmitter and a beam receiver. In operation, the beam transmitter is positioned to transmit a light beam towards the windshield. The windshield reflects the transmitted light beam as a function of the amount of precipitation on the windshield. The beam receiver is positioned to receive the reflected light beam. The amount of precipitation on the windshield is then determined as a function of the reflected light beam received by the beam receiver.
Commonly assigned U.S. Pat. No. 5,543,923 discloses an optoelectronic sensor device. This sensor device includes a beam guide body and associated pairs of beam transmitters and beam receivers. Pairs of lenses are arranged as part of the beam guide body. A first lense of each lense pair is associated with a respective beam transmitter and a second lense of each lense pair is associated with a respective beam receiver. In general, each beam transmitter transmits light beams to the windshield via the associated first lense and each beam receiver receives light beams reflected from the windshield via the associated second lense. As such, the first lenses serve to parallelize divergent light beam bundles transmitted from the associated beam transmitters and the second lenses serve to focus the parallel bundle of light beams reflected from the windshield onto the beam receivers.
This sensor device further includes a heating device. The heating device is arranged on a side of the beam guide body facing away from the windshield. The heating device is a positive temperature coefficient (PTC) thermistor or heating foil and is used to heat the sensor device in order to bring it to a sufficient operating temperature such as 40° C.
The heating device arrangement disclosed in U.S. Pat. No. 5,543,923 requires the use of relatively elaborate and costly special components. Further, this heating device arrangement results in blocking the penetration of ambient light into the inside of the sensor device over a relatively large area. Such ambient light blocking especially occurs in an effective design in which the heating device is flat and extends parallel to the windshield. The blocking of ambient light into optoelectronic sensor devices is undesirable at times. As such, in the case of a heating device arrangement blocking ambient light, the sensor device requires an ambient light receiving area that is located outside of the area shaded by the heating device. However, adding such an ambient light receiving area enlarges the total dimensions of the sensor device which is generally considered as being disadvantageous.